Cross flow machine



Jan. 3, W67 N.LAING 3,2957% CROSS FLOW MACHINE Original Filed June 5, 1962 5 Sheets-Sheet 1 y y INVENTOR f NIKOLAUS iLAiNG LT-X--M- ATTORNEYS Jam 3,, 1967 LA|NG 3395,?56

GROSS FLOW MACHINE Original Filed June 5, 1962 r 5 Sheets-Sheet 2 0 INVENTOR NIKOLAUS LAING ATTORNEYS Jan, 3, 1%? N. MING gwmm CROSS FLOW MACHINE Original Filed June 5, 1962 5 Sheets-Sheet 3 INVENTOR NIKOLAUS LAING vBY. EM, M T- XM ATTORNEYS United States Patent 3,295,750 CROSS FLOW MACHINE Nikolaus Laing, Stuttgart, Germany, assignor, by mesne assignments, to Laing Vortex, inc, New York, NY. Original application June 5, 1962, Ser. No. 221,621, new Patent No. 3,232,522. Divided and this application Jan. 28, 1966, Ser. No. 523,728

7 Claims. (Cl. 230-425) This invention relates to machines for inducing movement of fluids (which is to be understood as including both liquids and gases) and this application is a division of copending application Serial No. 221,621, filed September 5, 1962, now Patent No. 3,232,522, itself a continuation-in-part of application Serial No. 671,114, filed, July 5, 1957 and now abandoned. The invention concerns more particularly cross-flow fluid machines, that is, machines of the type comprising a hollow cylindrical bladed rotor mounted for rotation about its axis and through which, in operation of the machine, fluid passes at least twice through the path of the rotating blades in a direction transverse to the axis of the rotor.

The invention is particularly but not exclusively concerned with flow machines adapted to operate under conditions of low Reynolds numbers. The Reynolds numher at a particular fluid flow condition is a dimensionless number representing the ratio of the product of flow velocity and a characteristic linear dimension of the part under observation to the kinematic viscosity of the fluid. For the purpose of the present application Reynolds number (Re) will be defined as where d is the blade depth radially of the rotor, c is the peripheral speed of the rotor, and v is the kinematic viscosity of the fluid, the latter being equal to the quotient of the dynamic viscosity and density. A Reynolds number is considered herein to be low if, as above defined, it is less than x10 From the definition just given, it will be understood that flow machines operating under low Reynolds num ber conditions are small dimensionally, run at low peripheral speeds, or are intended for use with air or other gas having a low density or used with a fluid having a high viscosity.

For reasons which .are explained in my prior application Serial No. 221,621, it has previously been considered that the operation of conventional rotary type flow machines under conditions of low Reynolds numbers would necessarily and inescapably involve low efliciencies in comparison with efiiciencies obtainable under conditions of high Reynolds numbers. For example, although the inefficiency of small blowers has been notorious, it has been tolerated simply because it has not hitherto been thought capable of improvement.

rapidly to zero at the other side. It has also been assumed 'hitherto that a crossflow machine of the type described should always have the blades loaded approximately equally by the fluid in the circumferential zones where the fluid passes through the rotor blades. These two related conditions can normally be satisfied without much difficulty.

The invention depends in part on the appreciation that contrary to what has previously been thought by those skilled in the art, it can be advantageous to bring about in a cross-flow machine a velocity profile having a pronounced maximum with a consequent very unequal loading of the blades in the circumferential zones through which fluid passes. This velocity profile with a pronounced maximum gives rise to some flow tubes within the blower having much greater velocity than the other flow tubes within the blower.

In the restricted circumferential zones of the rotor blades through which the high velocity flow tubes pass, correspondingly high relative velocities exist locally between the fluid and the blades, so that in these zones momentum is imparted to the fluid at etficiencies which could otherwise be obtained only with machines operating under conditions of correspondingly much higher Reynolds numbers. The velocity profile with a pronounced maximum leads to lower velocities than the mean velocity in other circumferential zones of the rotor blades and in these zones transfer of momentum occurs at an efliciency which is lower than it would have been had the velocity profile been rectangular. However, the available momentum in a flowing tube issuing from the blades increases With the third power of its velocity, thus the momentum of the fluid as a whole is therefore substantially concentrated in the high velocity flow tubes so that the transfer efficiencies in the zones of slow through-flow have little effect on the over-all efficiency.

The invention depends in part further on the appreciation that the above-mentioned velocity profile with a pronounced maximum can be obtained by setting up in the machine a substantially cylindrical fluid vortex including a field region with a velocity profile approximating that of a Rankine vortex having a core interpenetrating the path of the blade envelope formed when the rotor rotates and that the throughput of the machine may be varied by controlling the intensity of the vortex.

The invention further depends in part on the appreciation that performance of the flow machine, by which is meant the throughput and pressure, can be optimized by reducing the size of the vortex core region.

The invention accordingly provides a fluid flow machine comprising a cylindrical bladed rotor defining an interior space clear of obstruction and mounted for rotation in a predetermined direction about its axis, the blades being curved and having their outer edges leading their inner edges in said predetermined direction, means substantially closing the ends of the rotor, and guide means defining with the rotor entry and discharge regions and comprising end walls .in substantial alignment with the ends of the rotor and first and second guide walls extending between the end walls and defining an outlet duct for fluid leaving the rotor. According to the invention the first guide wall presents to the rotor an end surface which subtends at the rotor axis an angle of less than 30 preferably less than 15: the

wall is conveniently, though not necessarily, in the form of a plate, with its edge towards the rotor and well spaced therefrom. Further according to the invention the first guide wall as seen in cross section forms a profile which if continued towards the rotor beyond the end surface would be substantially tangential to the rotor at a point intermediate in the arc thereof within the discharge region: the profile may be straight or curved, and is preferably such as to be tangential to the rotor at a point which lies nearer to the first guide wall than to the point of nearest approach of the second guide wall to the rotor. The effect of these features, in combination with the form of second guide wall to be discussed below, is that in operation of the guide means and rotor cooperate to set up and stabilize a vortex of Rankine type which has a core region of relatively small size interpenetrating the path of the rotating blades of the rotor adjacent the end surface of the first guide wall. This vortex induces a flow of fluid from the entry region through the path of the rotating blades to the interior of the rotor and thence again through the path of the rotating blades to the discharge region and through the outlet duct with the major part of the fluid throughput being turned through an angle approaching 180 in passing from the entry region to said outlet duct.

In general the turning of the major part of the flow through an angle approaching 180 corresponds to a small vortex core region and indicates the existence of a velocity profile having a pronounced maximum at the periphery of the core region. These have been formed the conditions for optimum throughput and pressure. If the first guide wall presents to the rotor a surface which subtends a large angle at the rotor axis the vortex core region tends to become enlarged, and the velocity profile becomes flatter. Though this may be suitable for some applications, it does not produce the best performance. Undue prolongation of this surface may render the performance inadequate for any normal purpose.

The performance of the machine is reduced and its noise increased by pockets of random eddies. Restricting the surface presented to the rotor by the first guide wall helps to reduce eddies on the entry side. Making the profile of this wall tangential to the rotor tends to reduce random eddying on the discharge side, and enables the maximum velocity flow tubes more readily to peel off from the periphery of the vortex core region and pass down the outlet duct adjacent the first guide wall.

According to the invention the second guide wall forms a generally spiral line starting from a point of nearest approach to the rotor opposite the end surface of the first guide wall where the entry and discharge regions merge. It is important not to have any substantial arc of the rotor closed off by the second guide wall. Preferably the guide wall diverges steadily from the rotor going in the direction of rotation. Like the first guide wall it is preferably well spaced from the rotor.

Various embodiments of the invention will now be described with reference to the accompanying diagrammatic drawings: in which FIGURE 1 is a cross-sectional view of a fluid ma chine in accordance with the invention;

FIGURE 2 is a graph illustrating velocity of fluid flow at the outlet of a cross-flow fluid machine utilizing a fluid vortex for guiding in part the flow through the rotor of the machine;

FIGURE 3 is a graph illustrating the velocity of fluid flow at the outlet of a conventional machine;

FIGURE 4 is a graph illustrating velocity of fluid flow within the field and core of the Rankine type fluid vortex;

FIGURE 5 illustrates the ideal fluid flow occurring in one half the cross-sectional area of a rotor of a fluid machine constructed according to the invention;

FIGURE 6 is a vector diagram illustrating flow of fluid contacting a blade of rotor of a machine constructed according to the invention where the fluid is passing from the interior of the rotor to the exit side of the machine;

FIGURES 7, 8 and 9 are views similar to FIGURE 1 showing three further forms of fluid flow machine, according to the invention;

FIGURE 10 is a view similar to FIGURE 9 showing the flow machine thereof adjusted for recirculation of fluid, and

FIGURE 11 is a graph explaining the functioning of the machine of FIGURES 9 and 10.

Referring first to FIGURE 1, the flow machine there shown comprises a cylindrically bladed rotor 2 having thereon a plurality of blades 3 concavely curved in the direction of rotation of the rotor indicated by the arrow 4 wherein the blades 3 have their outer edges 5 leading their inner edges 6. The outer edges define an outer envelope 7 while the inner edges define an inner envelope 8 when the rotor is rotated. The rotor is mounted, by means not shown, whereby it will rotate about its axis. First and second guide walls 9, 10 extend the length of the rotor and form an exit duct 11 of the machine in the form of a diffuser.

The guide walls 9 and 1t} serve to separate the suction side S from the pressure side P of the machine and to define an entry and an exit region to the rotor. End walls 13, only one of which is shown, substantially cover the ends of the machine.

The first guide wall 9 has the form of a thick plate and presents a rounded end surface 15 to the rotor, this surface subtending an angle at the rotor axis of well under 15 The wall 9 presents to the exit duct 11 a surface 14 the profile of which is shown continued towards the rotor beyond the end surface 15 by the dotted line 16, which is tangential to the rotor envelope 7 at a point 17 in the exit region nearer the guide wall 9 than the guide wall It].

The wall 10 is of spiral formation and starts at point 20 which is opposite the guide wall 9 and diverges steadily from the rotor going in the direction of rotation. At the point 20 the wall is spaced from the rotor a minimum of one-third the blade depth and not more than three times the blade depth of the blades 3. This spacing minimizes interference which causes an undesirable noise when the machine is operated while at the same time the wall provides a means to guide the flow leaving the machine. The end surface 15 of the guide wall 9 likewise is spaced a substantial distance from the rotor, in this instance a distance equal to a minimum distance of at least onethird the blade depth of the blades of the rotor. Because both the walls 9 and 10 are spaced from the latter a substantial distance, close manufacturing tolerances do not have to be observed when assembling the machine and, as such, the machine lends itself to economical construction such as is achieved when sheet metal stampings are utilized.

It is to be noted that the guide walls 9, 10, and in par ticul-ar the latter, do not close off flow to any part of the rotor, such as would be the case by a wall portion closely overlying the rotor. At the .point 20 the pressure and suction sides of the fan merge.

In operation of the fluid machine illustrated in FIG- URE 1, a fluid vortex having a core designated by the line V approximating a Rankine type vortex is formed wherein the core is positioned eccentrically with respect to the rotor axis and wherein the core will interpenetrate the path of the rotating blades of the rotor adjacent the end surface 15. The whole throughput of the machine will then flow twice through the blade envelope in a direction perpendicular to the rotor axis indicated by the flow lines F, MF.

FIGURE 4 illustrates an ideal relation of the vortex to the rotor 2 and the distribution of flow velocity in the vortex and in the field of the vortex. The line 4%) represents a part of the inner envelope 6 of the rotor blades 3 projected onto a straight line while the line 41 represents a radius of the rotor taken through the axis of the vortex core V. Velocity of fluid at points on the line 41 by reason of the vortex is indicated by the horizontal lines 43a, 43b, 43c and 430., the length of these lines being the measure of the velocity at the points 43a 4317 430 and 43:1 The envelope of these lines is shown by the curve 44 which has two portions, portion 44a being approximately a rectangular hyperbola and the otherportion, 4412, being a straight line. Line 44a relates to the field region of the vortex and the curve 441: to the core. It will be understood that the curve shown in FIGURE 4 represents the velocity of fluid where an ideal or mathe matical vortex is formed, and that in actual practice, flow conditions will only approximate these curves' The core of the vortex is a whirling mass of fluid with no translational movement as a whole and the velocity diminishes from the periphery of the core to the axis 42. The core of the vortex intersects the blade envelope as indicated at 40 and an isotach I within the vortex having the same velocity as the inner envelope cont-acts the envelope. The vortex core V is a region of low pressure and the location of the core in a machine constructed according to the invention can be determined by measurement of the pressure distribution within the rotor.

The velocity profile of the fluid where it leaves the rotor and passes through the path of the rotating blades will be that of the vortex. In the ideal case of FIGURE 4, this profile will be that of the Rankine vortex there shown by curves 43a and 43b, and in actual practice, the profile will still be substantially that shown in FIGURE 4 so that there will be in the region of the periphery of the core V shown in FIGURE 1 a flow tube MP of high velocity and the velocity profile taken at the exit of the rotor will be similar to that shown in FIGURE 2 where the line FG represents the exit of the rotor and the ordinates represent velocity. The curve shown exhibits a pronounced maximum point C which is much higher than the average velocity represented by the dotted line.

It will be appreciated that much the greater amount of fluid flows in the flow tubes in the region of maximum velocity. It has been found that approximately 80% of the flow is concentrated in the portion of the output represented by the line AE which is less than 30% of the total exit of the rotor. A conventional velocity profile for fluid flow in a defined passage is illustrated by way of contrast in FIGURE 3 where the average velocity of flow is represented by the dotted line. Those skilled in the art regard this profile as being approximately a rectangular profile which following the principle generally adhered to is the sort of profile heretofore sought in the outlet of a flow machine.

The maximum velocity C shown in FIGURE 2 appertains to the maximum velocity flow tube indicated as ME in FIGURE 1. With a given construction the physical location of the flow tube MF maybe closely defined. The relative velocity between the blades and fluid in the restricted zone of the rotor blades 3 through which the flow tube MF passes is much higher than it would be if a flow machine were designed following the conditions adhered to heretofore in the art respecting the desirability of a rectangular velocity profile at the exit arc and even loading of the blades.

Under low Reynolds number conditions, this unevenness of the velocity profile leads to beneficial results in that there will be less separation and energy loss in the restricted zone through which the flow tube MF passes than if that flow tube had the average velocity of throughput taken over the whole exit of the rotor. There is a more efficient transfer of momentum to the fluid by the blades in this restricted zone and while the transfer of momentum in the flow tubes travelling below the average velocity will be less efficient, nevertheless when all of the flow tubes are considered, there is a substantial gain in efficiency.

FIGURE 5 illustrates the ideal distribution of flow tubes F occurring within one half the rotor area defined by the inner envelope 6, it being understood that the flow tubes in the other half of the rotor are similar. The maximum velocity flow tube MF is shown intersecting the envelope 6 at point 50 and the isotach I as being circular when the whole rotor is considered. It is seen that ideally the maximum velocity flow tube MF undergoes a change of direction of substantially 180 from the suction to the pressure sides when the flow in the whole rotor is considered. It is also to be noted that the major part of throughput, represented by the flow tube MF, passes through the rotor blades where they have .a component of velocity in a direction opposite to the main direction of flow within the rotor indicated by the arrow A.

FIGURE 6 is a diagram showing the relative velocities of flow withrespect to a blade at the point 50 referred to in FIGURE 5. In this figure V represents the velocity of the inner edge of the blade 3 at the point 50, V the absolute velocity of the air in the flow tube MF at the point 50, and V the velocity of that air relative to the blade as determined by completing the triangle. The direction of the vector V coincides with that of the blade at its inner edge so that fluid flows by the blade substantially without shock.

The character of a vortex is considered as being determined largely by the blade angles and curvatures. The position of the vortex, on the other hand, is considered as being largely determined by the configuration of the vortex forming means which forms and stabilizes a vortex in cooperation with the bladed rotor. The particular angles and curvatures in any given case depend upon the following parameters: the diameter of the rotor, the depth of a blade in a radial direction, the density and viscosity of the fluid, the disposition of the vortex forming means and the rotational speed of the rotor, as well as the ratio between overall pressure and back pressure. These parameters must be adapted to correspond to the operating conditions in a given situation. Whether or not the angle and shape of the blades have been fixed at optimum values is to be judged by the criterion that the flow tubes close to the vortex core are to be deflected substantially greater than It is to be appreciated that the flow lines of FIGURE 1 do not correspond exactly to the position of the vortex core V as illustrated in FIGURES 4 and 5 which represent the theoretical or mathematical flow. These latter figures show that it is desirable to have the axis of the core of the vortex within the inner blade envelope 6 so that the isotach within the core oscillates that envelope.

This position is not essential, and in fact, is not achieved in the structure shown in FIGURE 1.

It is to be further appreciated that despite the divergence of the flow in FIGURE 1 from the ideal, the maximum velocity flow tube MF with which is associated the major part of the throughput is nevertheless turned through an angle of substantially in passing from the suction to the pressure side of the rotor and that this maximum flow tube passes through the rotor blades where the blades have a velocity with a component opposite to the main direction of flow through the rotor as indicated by the arrow A.

Though the character of the vortex is believed chiefly dependent on the design of the blades it is by no means wholly so, and indeed poor design of the surrounding guide means can prevent any useful vortex from being formed at all. It has been found that in general optimum performance occurs when the major portion of the flow is deflected by an angle approaching 180, as illustrated in FIGURE 1. This deflection can be achieved, with appropriate design in other respects, if the first guide wall presents an end surface to the rotor subtending only a small angle at the rotor axis, as also illustrated in FIG- URE 1. In the conditions of FIGURE 1, the vortex core region is relatively small, with the major part of the throughput associated with the fiow line MF entering and leaving the rotor tangentially to the core region without obstruction by the guide wall. The small vortex core region has been found associated with a greater peak in the velocity profile and from the foregoing discussion it will be appreciated that this promotes efficiency of operation. Besides subtending a small angle at the rotor axis, the guide wall 9 has, as explained, a profile which is tangential to the rotor periphery. This has been found to facilitate flow of the high velocity flow tubes out of the rotor and through the outlet duct by peeling off the high velocity flow from the vortex core region and guiding it through the outlet duct. The profile described minimizes the formation of pockets of random eddies which represent a loss of energy.

Attention is also drawn to the spiral formation and wide spacing of the second guide wall 10 which ensures that discharge can take place from the rotor without hindrance thereby.

Optionally, the outlet duct 11 is subdivided by walls 23, 24 into separate diffuser channels as illustrated in FIGURE 1.

Turning now to FIGURES 7, 8 and 9, these figures illustrate flow machines having important features in common with that of FIGURE 1 and operating in a generally similar manner. which correspond to those of FIGURE 1 will be given the reference numerals used in FIGURE 1, and only major differences or additional features will be discussed. It will be understood that the general remarks given above will also apply to the embodiments of FIGURES 7, 8 and 9'.

The FIGURE 7 machine has adjacent a first guide wall 70 a flap 71 pivotally mounted for angular movement about axis 72 whereby the flap may be moved outwardly to shut off flow of the high velocity flow tube MF entering the rotor. The vortex there shown is formed and stabilized in the same manner as in the machine shown in FIGURE 1 so that when the flap is in the extended position, the major part of flow through the machine will be shut off with only a minor part entering the rotor through that portion which is radially opposite the high velocity flow tubes.

The machine illustrated in FIGURE 8 shows a means for admitting air from the inlet or suction side of the machine so that it will coincide with the periphery of the vortex core to increase its intensity. The first guide wall 80 shown has a wall 81 conforming to the rotor curvature over an arc of substantially 10, and a second wall 82 on the entry side which is concave thereto and which intersects the wall 81 at an obtuse included angle. An auxiliary body member 83 is spaced from the wall 82 to define therewith a channel 84 to guide fluid from the inlet S into the rotor at a desired angle. The arrangement of the structure is such that fluid entering the rotor through the channel 84 is directed to coincide with the periphery of the vortex core V and so forms part of the high velocity tube MF. In the structure shown in FIG- URE 10, the machine comprises a fixed body member 100 cooperating with a movable body member 101 to form, as shown in FIGURE 10, a composite first guide wall in the form of a thick plate and fulfilling the same function as the wall 10 in FIGURE 1. The body 101 has a wall surface 103 which in the position of the body shown is aligned with the wall surface 104 of the body 100 to form a side wall to the exit duct 11 of the machine to guide the flow tube MF away from the rotor, similarly to the wall 14 of FIGURE 1. As in previous embodiments, the composite wall here shown has a profile 16 which is tangential to the rotor, as illustrated.

When the movable body 101 is pivoted about axis 106 to the position as shown in FIGURE 10, the rounded end adjacent the rotor 1 presents approximately the same profile to the fluid leaving the rotor so that the vortex continues to be formed and remains substantially in the Parts in FIGURES 7, 8 and 9' same position as shown in FIGURE 10. The high velocity tube MF, however, is no longer guided to the outlet of the machine by the walls 103 and 104, but instead is guided back to the entry side of the rotor through passage 107 formed by wall 108 of body 101 and wall 109 of body to again reenter the rotor on the suction side of the machine, and in so doing, it forms a closed circuit as indicated in FIGURE 10. As a result of this construction, the throughput of the rotor exceeds that of the machine as av whole with the throughput of the machine being only that flow which is not recirculated back to the suction side and which, as indicated previously, comprises only a proportion of the total throughput of the rotor.

FIGURE 11 represents a comparison of the fluid pressure difference across a machine constructed according to the invention with the throughput volume I represents the average pressure difference between the suction and pressure sides of the machine and Q represents the throughput volume. The curve represents the comparison of fluid pressure difference with throughput volume when the machine of FIGURE 9 has the means 101 in the position shown. The curve 121 represents the pressure difference across the machine when the movable part 101 takes the position shown in FIGURE 10 where it is seen that change in throughput has little efie-ct on pressure since a part of the throughput is being recirculated back to the inlet. This characteristic is important where several machines such as that shown in FIG- URES l0 and 11 are operated in parallel where it is desired that the pressure in the circuits be substantially the same.

In general, the FIGURE 10 position will be used only under conditions of severe throttling (which term is intended to include the imposition of static pressure head across the machine, as by a choked filter at inlet or outlet). For many applications the FIGURE 9 arrangement can be used exclusively and in such case the bodies 100, 101 could be permanently joined.

I claim:

1. A fluid flow machine comprising a cylindrical bladed rotor defining an interior space clear of obstructions and mounted for rotation in a predetermined direction about its axis, the blades being curved and having their outer edges leading their inner edges in said predetermined di rection, means substantially closing the ends of the rotor, and guide means defining with the rotor, entry and discharge regions and comprising end walls in substantial alignment with the ends of the rotor; first and second guide walls extending between the end walls and defining an outlet duct for fluid leaving the rotor, said first guide wall presenting to the rotor an end surface which subtends at the rotor axis an angle of less than 30 and as seen in cross-section forming a profile which, if continued beyond said surface would be substantially tangential to the rotor at a point intermediate in the arc thereof within said discharge region, the second guide wall as seen in cross section forming a general spiral line starting from a point of nearest approach to the rotor opposite said first guide wall where said entry and discharge regions merge, the end surface of said first guide wall and rotor on rotation thereof in said predetermined direction cooperating to set up and stabilize a vortex of Rankine type which has a core region that is eccentric of the rotor axis and interpenetrates the path of the rotating blades of the rotor adjacent said surface of the first guide wall and induces a flow of fluid from the entry region through the path of the rotating blades to the interior of the rotor and thence again through the path of the rotating blades to the discharge region and through the outlet duct with the major part of the fluid throughput being turned through an angle approaching in passing from the entry region to said outlet duct.

2. A machine as claimed in claim 1, wherein said surface presented by the first guide wall to the rotor subtends at the rotor axis an angle less than 15.

3. A machine as claimed in claim 2, wherein said first guide wall is plate-like and said surface presented to the rotor is an edge of the plate.

4. A machine as claimed in claim 1, said line formed by the first guide wall being a straight line.

5. A machine as claimed in claim 4, said line formed by the first guide wall being a curved line.

6. A machine as claimed in claim 1, wherein said line formed by the first guide wall would be tangential to the rotor at a point nearer said surface presented by the first guide Wall to the rotor than to the point of nearest approach of the second guide wall to the rotor.

7. A machine as claimed in claim 1, wherein the sec ond guide wall diverges from the rotor starting immediately from its line of nearest approach thereto.

References Cited by the Examiner UNITED STATES PATENTS 2,339,575 1/1944 Lee 230-125 FOREIGN PATENTS 527,700 4/1954 Belgium.

MARK NEWMAN, Primary Examiner.

HENRY F. RADUAZO, Assistant Examiner. 

1. A FLUID FLOW MACHINE COMPRISING A CYLINDRICAL BLADED ROTOR DEFINING AN INTERIOR SPACE CLEAR OF OBSTRUCTIONS AND MOUNTED FOR ROTATION IN A PREDETERMINED DIRECTION ABOUT ITS AXIS, THE BLADES BEING CURVED AND HAVING THEIR OUTER EDGES LEADING THEIR INNER EDGES IN SAID PREDETERMINED DIRECTION, MEANS SUBSTANTIALLY CLOSING THE ENDS OF THE ROTOR, AND GUIDE MEANS DEFINING WITH THE ROTOR, ENTRY AND DISCHARGE REGIONS AND COMPRISING END WALLS IN SUBSTANTIAL ALIGNMENT WITH THE ENDS OF THE ROTOR; FIRST AND SECOND GUIDE WALLS EXTENDING BETWEEN THE END WALLS AND DEFINING AN OUTLET DUCT FOR FLUID LEAVING THE ROTOR, SAID FIRST GUIDE WALL PRESENTING TO THE ROTOR AN END SURFACE WHICH SUBTENDS AT THE ROTOR AXIS AN ANGLE OF LESS THAN 30* AND AS SEEN IN CROSS-SECTION FORMING A PROFILE WHICH, IF CONTINUED BEYOND SAID SURFACE WOULD BE SUBSTANTIALLY TANGENTIAL TO THE ROTOR AT A POINT INTERMEDIATE IN THE ARC THEREOF WITHIN SAID DISCHARGE REGION, THE SECOND GUIDE WALL AS SEEN IN CROSS SECTION FORMING A GENERAL SPIRAL LINE STARTING FROM A POINT OF NEAREST APPROACH TO THE ROTOR OPPOSITE SAID FIRST GUIDE WALL WHERE SAID ENTRY AND DISCHARGE REGIONS MERGE, THE END SURFACE OF SAID FIRST GUIDE WALL AND ROTOR ON ROTATION THEREOF IN SAID PREDETERMINED DIRECTION COOPERATING TO SET UP AND STABILIZE A VORTEX OF RANKINE TYPE WHICH HAS CORE REGION THAT IS ECCENTRIC OF THE ROTOR AXIS AND INTERPENETRATES THE PATH OF THE ROTATING BLADES OF THE ROTOR ADJACENT SAID SURFACE OF THE FIRST GUIDE WALL AND INDUCES A FLOW OF FLUID FROM THE ENTRY REGION THROUGH THE PATH OF THE ROTATING BLADES TO THE INTERIOR OF THE ROTOR AND THENCE AGAIN THROUGH THE PATH OF THE ROTATING BLADES TO THE DISCHARGE REGION AND THROUGH THE OUTLET DUCT WITH THE MAJOR PART OF THE FLUID THROUGHPUT BEING TURNED THROUGH AN ANGLE APPROACHING 180* IN PASSING FROM THE ENTRY REGION TO SAID OUTLET DUCT. 